1. HISTORY OF ASTRONOMY REVISED!

2. Skylab – Stage 2 Get 75% of points back if you are improving your observational data – or anything else

3. Derivation Angle at A: α=19°Angle at A: α=19° Angle at B: β=22°Angle at B: β=22° Baseline (b): 12.6mBaseline (b): 12.6m Height (H): ???Height (H): ??? Have triangle with known side and 2 angles:Have triangle with known side and 2 angles: H = D tan β H = (D+b) tan α 2 equations, 2 unknowns Solve for H = b tan α/(1-tan α/tan β) A B D Excel Sheet

4. Example Angle at A: 19°Angle at A: 19° Angle at B: 22°Angle at B: 22° Baseline: 12.6mBaseline: 12.6m Height: 29.4ft = 96 ftHeight: 29.4ft = 96 ft A B

5. Performing Experiments Experiments must be repeatable – requires careful control over variables Possible outcomes of an experiment: –The experiment may support the theory We then continue to make predictions and test them –The experiment may falsify the theory We need a new theory that describes both the original data and the results of the new experiment Since we cannot do every possible experiment, a theory can never be proven true; it can only be proven false

6. Making Measurements Errors –Random –Systematic With every measurement, it is essential to provide an estimate of the uncertainty – the likely range of errors Example: –Using a ruler marked in mm, we round to the nearest marking – at most off by half a division, or 0.5 mm –Cite a measurement of 15 mm as 15  0.5 mm to indicate that the real value of the length is likely to be anywhere between 14.5 mm and 15.5 mm –If a theory predicts a value of 15. 2 mm, then a reading of 15  0.5 mm is in agreement with the theory but a reading of 15  0.1 mm is probably not

7. Is the uncertainty small or big? It depends! If you have a small uncertainty and the measured length is also small, you might have a huge uncertainty! Use percentages: –Percent error = (estimated uncertainty)/(result) x 100% –Example: 51.3 cm ± 0.2 cm gives –Percent error = (0.2 cm)/(51.3cm) x 100 % = 0.4 % (This is a pretty small uncertainty)

8. Is the result precise or accurate or what? Two different concepts: precision and accuracy! High precision means small error High accuracy means close to an accepted value Examples: * * * * high precision, high accuracy * * * * high precision, low accuracy * * * * low precision, high accuracy * * * * low precision, low accuracy accepted value

9. When do results agree? Results agree, if they are within the error margins of each other Examples: | O | values very different, but errors large: agreement! | O | values closer, but errors smaller: no agreement!

10. Triangulating the Size of the Earth Eratosthenes (ca. 276 BC) –Measures the radius of the earth to about 20%

11. Calculation Angle is measured to be 7.2 = 360/50 So distance Alexandria- Syene is 1/50 of Earth’s circumference Baseline can be measured: 5000 stades  Circumference is 23,330 miles (modern value: 25,000 miles – only 7% off

12. Distances to the Stars Use even bigger baseline by waiting ½ year, not ½ day Baseline: 300 million km Parallax can be used out to about 100 light years The bigger the parallactic angle, the closer the star! –A star with a measured parallax of 1” is 1 parsec away –1 pc is about 3.3 light years The nearest star (Proxima Centauri) is about 1.3 pc or 4.3 lyr away

13. The most important measurement in Astronomy: Distance! The distances are astronomical – of course The distance scales are very different –Solar system: light minutes –Stars: light years –Galaxies: 100,000 ly –Universe: billions of ly Need different “yardsticks”

14. A Short History of Astronomy Ancient (before 500 BC) –Egyptians, Babylonians, Mayans, Incas, Chinese Classical Antiquity (500 BC-500 AD) –Greeks, Romans: Plato, Aristotle, Ptolemy Middle Ages (500-1450 AD) –Arabic astronomers Renaissance (1450-1550 AD) –Copernicus Baroque (1550-1700 AD) –Brahe, Kepler, Galilei, Newton

15. Ancient Astronomy Stonehenge, England Pyramids, Gizeh near Cairo, Egypt

17. Aristotle (384 – 322 BC) Arguably the first genuine scientist in history Aristotle's views on physical science shaped medieval scholarship  Scholasticism His views on motion of the objects was deeply flawed but compelling Thomas Aquinas made Aristotle compatible with Christian beliefs

18. Physics and Metaphysics Aristotle’s “Physics” (Greek: Φυσικ ὴ ἀ κρόασις or physikes akroasis; Latin: Physica) is one of the foundational books of science and philosophy His book on philosophy is called Metaphysics (Greek: τ ὰ μετ ὰ τ ὰ φυσικά) – beyond physicsGreek

19. How do things move? Aristotle (c. 350 B.C.) Aristotle observed how things move, and constructed the following theory : Things have a tendency to stay stationary. If you push something, it will move, then return to it’s natural state: stationary. Actually, it will try to return to it’s natural place: smoke and gas will go up, rock and water will go down. If you fire an arrow from a bow, you give it impetus : it will travel until this impetus runs out, at which time it will fall to to ground and return to it’s natural state. This was stated in a series of books called ‘Physics’, and gives us the name of the science. This theory makes intuitive sense, and allows us to make a prediction: rocks won’t move unless they are pushed. People took this as truth for ~1900 years. Wrong, i.e. falsified by experiments!

20. Aristotle easily falsified by experiment – but emphasis was not on observation How people thought about projectiles up until the Renaissance: the cannonball moves in almost a straight line, until it runs out of impetus and falls on the house. WRONG!

21. Aristotle: On the Heavens Aristotle On astronomy Read in Latin throughout the middle ages Renaissance: Greek original

22. Two realms – eternally separated Sublunar: ever changing, complicated, chaotic, human (i.e. lowly) Supralunar: eternal, no changes other than “perfect” (i.e. complete) circular motion, divine

23. Prescientific Explanations - Alchemy See online reading Casual observation of patterns in nature –Bubbles of air in water go up, etc. Wrong theory/elements This leads to wrong world views

24. The Grand Mystification of the Cosmos Aristotle’s thoughts ossified and prevented progress Disempowerment of the inquisitive mind –Trapped in a realm of chaos, what can we do? –There is no connection of what goes on on Earth and in the heavens, so how can we find out? –We are lowly, how can we ask divine questions or question the word of God?

25. Sun, stand thou still! King James Bible (Joshua 10:12) Then spake Joshua to the LORD in the day when the LORD delivered up the Amorites before the children of Israel, and he said in the sight of Israel, Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon.King James Bible Logic: So the Sun usually moves!

26. The Bible, Plato, Aristotle, Ptolemy, Aquinas Everyone and the Scripture agree on the explanation of the cosmos since over one thousand years And you want to doubt that ?! How DARE you!